Dispersing agents used to incorporate mineral materials into thermoplastic resins have been known. Thus, the U.S. Pat. Nos. 4,412,026 and 5,001,182 disclose the use of fatty acids or their esters, as well as organic compounds of the silane or titanate type, as coupling agents in order to introduce up to 20% by weight of talc into the thermoplastic resin to obtain good object rigidity.
Also, it is well known that one can use compounds such as metallic salts of a fatty acid, for example calcium stearate (U.S. Pat. No. 4,255,303) or combinations of octyl or oxyethylated nonylphenol with polyoxyethylene glycols (U.S. Pat. No. 4,927,874 and U.S. Pat. No. 4,931,493) to treat talcs in order to incorporate them into thermoplastic resins. However, such processes allow one to obtain only filled compounds with degraded mechanical properties.
It is also known that one can use dispersing or treating agents that contain at least one unsaturated component (EP 7190 - GB 1,603,300) to treat mineral fillers with acid surface such as certain talcs. Such agents, however, are not particularly suitable for all types of talc.
There are also methods for the dispersion of pulverulent mineral fillers that use phosphonated dispersing agents (DE 2,735,160) or sulfonated dispersing agents (EP 0,017,038) or different methods (JP 80-142039, JP 78-65346, JP 75-109239) which allow the dispersion of certain talcs in polypropylene. However, in this case not all talcs are dispersed with the same efficiency in the polymer material that would thereby result in thermoplastic compounds with decreased physicochemical properties.
To date, thermoplastic compounds filled with talc are not entirely satisfactory concerning their viscosity level. These thermoplastic compounds do not allow one to carry out difficult manipulations during the fabrication of master batches or of plastic objects.